Fuel injector

ABSTRACT

The present invention relates to a fuel injector, particularly a high-pressure injection valve for the direct injection of fuel into a combustion chamber of an internal combustion engine having external ignition, which is distinguished in that an outlet orifice ( 23 ) is provided downstream from the valve seat ( 20 ) which, at its downstream end, has a slot-forming element ( 30 ) that largely closes off the outlet orifice ( 23 ). Between it and a front face ( 34 ) of the valve-seat member ( 16 ), the slot-forming element ( 30 ) leaves open a slot-shaped flow outlet ( 35 ), through which a fuel spray may be spray-discharged in a fan-jet pattern.

BACKGROUND INFORMATION

[0001] The present invention is directed to a fuel injector of the typeset forth in the main claim.

[0002] A fuel injector in which a slot-shaped outlet opening is providedat the downstream end is already known from DE 198 47 625 A1. The outletopening is either formed in a perforated disk or directly on the nozzlebody itself. The slot-shaped outlet openings are always introducedcentrally at the longitudinal valve axis. Upstream from the valve seatis a helical groove, which imparts a circular rotary motion to the fuelflowing to the valve seat. The flat outlet orifice ensures that the fuelis spray-discharged in a fanlike manner.

SUMMARY OF THE INVENTION

[0003] The fuel injector according to the present invention having thecharacterizing features of the main claim has the advantage over therelated art that fuel sprays in fan-jet form may easily be discharged inany desired spatial direction. The slot-shaped flow outlet provides thatthe jet penetrates to varying degrees across the width of the fan jet.This advantageously produces fan-type spray fronts which penetrate thecombustion chamber to varying depths during direct injection. Themaximally available combustion chamber cross-section is thereby filledwith fuel spray, without any significant wetting of thecombustion-chamber wall. The maximum air quantity is mixed with fuelspray, without any particular wall wetting.

[0004] Advantageous further refinements and improvements of the fuelinjector specified in the main claim are rendered possible by themeasures cited in the dependent claims.

[0005] The width of the flow outlet may be varied in an advantageousmanner since the cross-sectional area of the flow outlet changes as afunction of the hydraulic pressure acting on the slot-forming elementand the plastic deformation of the slot-forming element in the area ofthe free circumferential section that it entails. In this manner, theflow-rate of the valve (dynamic flow quantity) may be selectivelychanged and set. The dynamic range of a fuel injector is thereby able tobe advantageously enlarged toward small spray-discharge quantities. Evensmaller, precisely metered spray-discharge quantities are possible inidle operation at lowered system pressure.

[0006] The pressure-controlled variation of the width of the flow outletalso makes it possible to vary the width of the fan jet, that is, thepropagation angle of the jet fan. Since the slot-cross section islenticular, the mass-flow portion at the two pointed slot ends is lessthan the mass flow portion in the central region of the flow outlet. Ifthe slot width is reduced, the mass portion emerging at the two slotends is correspondingly lower yet, so that the slot length effectivelytraversed by the flow is reduced in response to a reduction in the slotwidth. Consequently, the propagation angle of the jet fan, given apressure drop, is likewise reduced. At low engine loads, this providesfor an appropriately reduced propagation of the spray cloud in thecombustion chamber, which meets power efficiency demands.

[0007] The static flow quantity may be adjusted via the width of theflow outlet. At the end of the valve manufacturing process, the slotwidth is adjusted by mechanical bending of the slot-forming element.

[0008] The danger of carbon deposits forming in the flow outlet isreduced by the pressure pulsations during valve operation, since theflow outlet “breathes”, due to the constant width variation. This“breathing” mechanically removes deposits in the area of the flowoutlet.

BRIEF DESCRIPTION OF THE DRAWING

[0009] Exemplary embodiments of the present invention are represented insimplified form in the drawing and are explained in detail in thefollowing description. The figures show:

[0010]FIG. 1 a partially represented fuel injector having a firstspray-discharge geometry in accordance with the present invention;

[0011]FIG. 2 the slot-forming element used in the fuel injectoraccording to FIG. 1, in a view from below;

[0012]FIG. 3 an idealized representation of a jet fan able to bespray-discharged by the fuel injector according to FIG. 1;

[0013]FIG. 4 a second example of a fuel injector, in the same view asFIG. 1;

[0014]FIG. 5 a plan view of a further slot-forming element;

[0015]FIG. 6 a section along the line VI-VI in FIG. 5; and

[0016]FIG. 7 a third example of a fuel injector in the same view as FIG.1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0017]FIG. 1 partially shows a valve in the form of an injector for fuelinjection systems of mixture-compressing, externally ignited internalcombustion engines, as an exemplary embodiment. The fuel injector isparticularly suitable as a high-pressure injector for the directinjection of fuel into a combustion chamber of an internal combustionengine. The injector shown in FIG. 1 has a tubular valve-seat support 1,in which a longitudinal opening 3 is formed concentrically to alongitudinal valve axis 2. Situated in longitudinal opening 3 is an e.g.rod-shaped valve needle 5, which is fixedly connected by way of itsdownstream end 6 to, for example, a spherical valve closure member 7, onwhose periphery, for example, five flattened regions 8 are provided forthe fuel to flow past.

[0018] The fuel injector is actuated in a known manner, e.g.electromagnetically. However, a piezoelectric actuator is also possibleas an excitable actuating element. Likewise, an actuation via a pistonsubjected to pressure in a controlled manner is also an option. Aschematically sketched electromagnetic circuit including a magnetic coil10, an armature 11 and a core 12 is used for axially moving valve needle5, and thus for opening a restoring spring (not shown) against thespring tension, or for closing the fuel injector. Armature 11 isconnected to the end of valve needle 5 facing away from valve-closuremember 7 by a welding seam that is formed by laser, for instance, andpoints to core 12.

[0019] A guide opening 15 of a valve-seat member 16, which is introducedin the downstream end 18 of valve-seat support 1 in longitudinal opening3, is provided to guide valve-closure member 7 during the axialmovement. Valve-seat member 16 is provided, for instance, with acircumferential flange 17, which extends under downstream end 18 ofvalve-seat support 1. Upper face 19 of circumferential flange 17 isground, for instance, in a clamping device, with guide opening 15 and avalve-seat surface 20 provided in valve-seat member 16. Valve-seatmember 16 is inserted until upper face 19 of flange 17 abuts against end18 of valve-seat support 1. Valve-seat member 16 is secured in thecontact region of the two components 1 and 16, for instance, by a weldedseam 22 produced by a laser.

[0020] Formed downstream from valve-seat surface 20, which, forinstance, tapers frustoconically in the flow direction, is an e.g.circular outlet orifice 23 in a valve-seat member 16, which ends in anat least partially projecting spray-discharge area 25. Outlet orifice 23is largely closed by a slit-forming element 30 provided at itsdownstream end which, in the exemplary embodiments, is configured as athin, membrane-type elliptical tongue in each case.

[0021] Slit-forming element 30 is mounted on valve-seat member 16, forinstance, by way of a welded seam 31. Welded seam 31 extends only acrosspart of the periphery of slot-forming element 30. In FIG. 2, which showsslot-forming element 30 used in the fuel injector according to FIG. 1 ina view from below, it can be seen that welded seam 31 wraps around morethan 50% of the circumference of slot-forming element 30. Ideally, thewelded circumference amounts to between 50 and 75% of the totalcircumference of slot-forming element 30. The remaining part of thecircumference of slot-forming element 30 is in the form of freecircumferential section 33.

[0022] While in the mounting area, i.e., in the region of welded seam31, slot-forming element 30, of necessity, directly abuts closelyagainst a lower front face 34 of spray-discharge area 25, lower frontend 34, in the area of free circumferential section 33 of slot-formingelement 30, is formed such that a slight gap exists with respect to oneanother between lower front face 34 and slot-forming element 30.Therefore, a slot-shaped flow outlet 35 is provided across 25 to 50% ofthe circumference of slot-forming element 30. Slot-forming element 30,for instance, is disposed at an angle, i.e., at an angle deviating fromlongitudinal valve axis 2 by 90°, so that a fuel spray to bespray-discharged may likewise emerge at an angle.

[0023] The width of flow outlet 35 may be varied in an advantageousmanner. That is because the cross-sectional area of flow outlet 35changes as a function of the hydraulic pressure acting an slot-formingelement 30 and the associated plastic deformation of slot-formingelement 30 in the area of free circumferential section 33. In thismanner, the flow rate of the valve (dynamic flow quantity) may beselectively modified and set.

[0024] Slot-shaped flow outlet 35 makes it possible to produce aso-called fan-jet pattern 37 that is particularly advantageous in thedirect injection of fuel into a combustion chamber 39 of an internalcombustion engine. Shown in idealized form in FIG. 3 is a spray patternthat may be produced. Slot-shaped flow outlet 35 ensures that the jetpenetrates to varying degrees across the width of fan jet 37. In thecentral region of flow outlet 35, fan jet 37 emerges with the largestmass portion or the strongest jet penetration, while the penetration islowest at the two slot ends 38. This produces fan-jet fronts 37′ whichadvantageously penetrate combustion chamber 39 to varying depths. Inthis manner, the maximally available combustion chamber cross-section isfilled with fuel spray, without any significant wetting of thecombustion-chamber wall 40. The maximum air quantity is mixed with fuelspray, without any particular wall wetting.

[0025]FIG. 4 shows a second example of a fuel injector, in the same viewas shown in FIG. 1. In this case, center spray-discharge area 25upstream from valve seat 20 has a clearly projecting form. Outletorifice 23 extends in two parts, a first section 23 a running axiallyparallel, and a second section 23 b forming an angle thereto, which, forexample, encloses an angle of approx. 50 to 70° that includeslongitudinal valve axis 2. Spray-discharge area 25 has a largelycylindrical shape with a lateral surface extending in parallel tolongitudinal valve axis 2. Correspondingly, slot-forming element 30likewise has an axially-parallel orientation and extends either in acurved manner in the circumferential direction or in a planar fashion ata flattened region of spray-discharge area 25. Due to the steep positionof slot-forming element 30, fan jet 37 emerges largely paraxially fromslot-shaped flow outlet 35.

[0026] If, for strength reasons, a greater structural stiffness isrequired for slot-forming element 30, slot-forming element 30 may alsobe implemented with a greater thickness. However, in that case the widthof slot-shaped flow outlet 35 may no longer be adjusted by bendingslot-forming element 30. It will then be necessary to obtain flow outlet35 through a trough-shaped depression 41 formed at slot-forming element30. FIG. 5 shows a plan view of the inflow side of such a slo-formingelement 30 having a depression 41. In an advantageous manner, depression41 is implemented as a circle sector at free circumferential section 33of slot-forming element 30, so that the opening angle of the circlesector specifies the propagation angle of fan-jet 37. The depression ismade by stamping, for example. FIG. 6 shows a section along line VI-VIin FIG. 5. Depression 41 extends over half of the thickness ofslot-forming element 30, for example. Flow outlet 35 is defined betweendepression bottom 42 of depression 41 and front face 34 of valve-seatmember 16.

[0027] The stiffness of membrane-type slot-forming element 30 may alsobe increased by another measure, which is shown in FIG. 7. To increasethe stiffness, a disk-shaped supporting element 43 is mounted directlybelow slot-forming element 30. Support element 43 only extends partiallyunder slot-forming element 30. In the supported region, support element43 prevents a bending of slot-forming element 30 due to pressure.However, in the non-supported region, slot-forming element 30 may stillbend in a desired form. The flexural stiffness of slot-forming element30 may be adjusted as desired in that the position of support element 43prior to its fixation may be specified as variable.

What is claimed is:
 1. A fuel injector for fuel injection systems ofinternal combustion engines, in particular for the direct injection offuel into a combustion chamber of an internal combustion engine,comprising a longitudinal valve axis (2), an actuator (10, 11, 12), amovable valve part (5, 7), which cooperates with a stationary valve seat(20) formed at a valve-seat member (16) to open and close the valve, andan outlet orifice (23) formed downstream from the valve seat (20) in thevalve-seat member (16), wherein a slot-forming element (30) whichlargely closes the outlet orifice (23) is located at the downstream endof the outlet orifice (23), leaving open a slot-shaped flow outlet (35)between itself and a front face (34) of the valve-seat member (16). 2.The fuel injector as recited in claim 1, wherein the slot-formingelement (30) has a membrane-type design.
 3. The fuel injector as recitedin claim 1 or 2, wherein the slot-forming element (30) has an ellipticalshape.
 4. The fuel injector as recited in one of the preceding claims,wherein the slot-forming element (30) is mounted directly on thevalve-seat member (16).
 5. The fuel injector as recited in claim 4,wherein the slot-forming element (30) is secured by a welded seam (31),and the welded seam (31) extends over 50 to 75% of the entirecircumference of the slot-forming element (30).
 6. The fuel injector asrecited in claim 4 or 5, wherein, outside of the fastening region (31),a free circumferential section (33) of the slot-forming element (30) isgiven, the flow outlet (35) being formed between it and the front face(34) of the valve-seat member (16).
 7. The fuel injector as recited inclaim 6, wherein the flow outlet (35) is implemented as a depression(41) in the slot-forming element (30).
 8. The fuel injector as recitedin one of the preceding claims, wherein the flow outlet (35) is locatedaway from the longitudinal valve axis (2).
 9. The fuel injector asrecited in one of the preceding claims, wherein the slot-forming element(30) is inclined at an angle, i.e. is positioned at an angle thatdeviates from the longitudinal valve axis (2) by 90°.
 10. The fuelinjector as recited in one of the preceding claims, wherein theslot-forming element (30) is plastically deformable during valveoperation and the width of the flow outlet (35) is thus variablyadjustable.
 11. The fuel injector as recited in one of the precedingclaims, wherein a disk-shaped support element (43) is mounted directlybelow the slot-forming element (30) to increase stiffness.